Journal of Medical Virology 84:1967–1974 (2012)

Response to Valganciclovir in Chronic Fatigue
Syndrome Patients With Human Herpesvirus 6
and Epstein–Barr Virus IgG Antibody Titers
Tessa Watt,1 Stephanie Oberfoell,1 Raymond Balise,2 Mitchell R. Lunn,3 Aroop K. Kar,1
Lindsey Merrihew,1 Munveer S. Bhangoo,1 and José G. Montoya1,2,4*
1
Division of Infectious Diseases and Geographic Medicine, Department of Medicine,
Stanford University Medical Center, Palo Alto, California
2
Stanford University School of Medicine, Health Research and Policy, Stanford, California
3
Stanford University School of Medicine, Stanford, California
4
Palo Alto Medical Foundation, Research Institute, Palo Alto, California

Valganciclovir has been reported to improvephysical and cognitive symptoms in patientswith chronic fatigue syndrome (CFS) with elevated human herpesvirus 6 (HHV-6) and
Epstein–Barr virus (EBV) IgG antibody titers.
This study investigated whether antibody titers
against HHV-6 and EBV were associated withclinical response to valganciclovir in a subset of
CFS patients. An uncontrolled, unblinded retrospective chart review was performed on 61 CFS
patients treated with 900 mg valganciclovir daily(55 of whom took an induction dose of
1,800 mg daily for the ﬁrst 3 weeks). Antibody
titers were considered high if HHV-6 IgG 1:320,
EBV viral capsid antigen (VCA) IgG 1:640, andEBV early antigen (EA) IgG 1:160. Patients selfrated physical and cognitive functioning as apercentage of their functioning prior to illness.
Patients were categorized as responders if theyexperienced at least 30% improvement in physical and/or cognitive functioning. Thirty-two
patients (52%) were categorized as responders.
Among these, 19 patients (59%) responded
physically and 26 patients (81%) responded cognitively. Baseline antibody titers showed nosigniﬁcant association with response. After
treatment, the average change in physical andcognitive functioning levels for all patients wasþ19% and þ23%, respectively (P < 0.0001). Longer treatment was associated with improved response (P ¼ 0.0002). No signiﬁcant difference
was found between responders and non-responders among other variables analyzed. Valganciclovir treatment, independent of thebaseline antibody titers, was associated with
self-rated improvement in physical and cognitive functioning for CFS patients who had positive HHV-6 and/or EBV serologies. Longer
valganciclovir treatment correlated with anß 2012 WILEY PERIODICALS, INC.

improved response. J. Med. Virol. 84:1967–
1974, 2012. ß 2012 Wiley Periodicals, Inc.
KEY WORDS: CFS; HHV-6; EBVINTRODUCTION
Chronic fatigue syndrome (CFS) is a controversial,multi-systemic disease that affects more than 1 million Americans [CDC, 2012], resulting in $9.1 billion
in lost productivity annually [Reynolds et al., 2004].
CFS is characterized clinically by severe disabling
fatigue and a constellation of symptoms that
Author contributions: T.W., S.O., A.K.K., and J.G.M. designed
the study. M.R.L. and J.G.M. provided patient care. T.W., S.O.,
A.K.K, and M.B. coordinated the study and collected the data.
T.W., S.O., and R.B. performed statistical analysis and analyzed
the data. T.W., S.O., R.B., M.R.L., L.M., and J.G.M. wrote themanuscript. J.G.M. supervised the project.
All authors have no ﬁnancial or other conﬂict of interest.
Tessa Watt and Aroop K. Kar present address is 5 Universityof Michigan Medical School, 1301 Catherine Road, Ann Arbor,
MI 48109.
Stephanie Oberfoell present address is Los Angeles David
Geffen School of Medicine, University of California, 1633 Bruin
Street, Los Angeles, CA 90047.
Mitchell R. Lunn present address is Department of Medicine,
Brigham and Women’s Hospital, 75 Francis Street, Boston, MA
02115; Harvard Medical School, 25 Shattuck Street, Boston, MA
02115.
Munveer S. Bhangoo present address is San Diego School of
Medicine, University of California, 8950 Villa La Jolla Drive,
San Diego, CA 92037.
*Correspondence to: José G. Montoya, Stanford University
School of Medicine, 300 Pasteur Drive, Room S-101, Stanford,
CA 94305. E-mail: gilberto@stanford.edu
Accepted 26 July 2012
DOI 10.1002/jmv.23411
Published online in Wiley Online Library(wileyonlinelibrary.com).

1968

prominently features impaired concentration andshort-term memory, sleep disturbances, and musculoskeletal pain. No pathognomonic signs or diagnostic
tests have been validated, and no deﬁnitive treatments
are available.
CFS is recognized as a complex clinical syndrome
with multiple presentations [Jason et al., 2005]. Proposed etiologies include viral or bacterial infections,environmental factors, endocrine and metabolic dysfunction, immunological imbalance, neural-mediatedhypotension, and depression [Fukuda et al., 1994; Afariand Buchwald, 2003]. A viral trigger has been suspected when patients developed acute CFS following
severe inﬂuenza-like symptoms, infectious mononucleosis, Q fever, or Ross River virus infection [Komaroff
and Buchwald, 1998; Hickie et al., 2006]. Human herpesvirus 6 (order Herpesvirales, family Herpesviridae,
subfamily Betaherpesvirinae, genus Roselolvirus, species Human herpesvirus 6; HHV-6) and Epstein–Barrvirus (order Herpesvirales, family Herpesviridae, subfamily Gammaherpesvirinae, genus Lymphocryptovirus, species Human herpesvirus 4; EBV or HHV-4) areamong the viruses that have been frequently associatedwith CFS [Komaroff, 1988, 2006; Kogelnik et al., 2006].
EBV and HHV-6 are lymphotrophic and produce latent infections with immunomodulatory effects[Ambinder, 2003; Krueger and Ablashi, 2003; Ambinderand Lin, 2005] In addition, HHV-6 has been found to beneurotropic [Ablashi et al., 2010; Flamand et al., 2010;
Yao et al., 2010] and can reside in neurons [Fotheringham et al., 2008] and cardiac myocytes [Kuhl et al.,2005; Leveque et al., 2011] in a semi-active state without evidence of continued infection in the plasma compartment. HHV-6 has been associated with cognitive
decline in hematopoietic stem cell transplantation, andit has been reported to cause encephalitis in 8–14% ofumbilical cord blood transplant patients [Mori et al.,2010; Hill et al., 2012]. While in vitro co-infection withboth viruses has revealed signiﬁcant interaction [Flamand et al., 1993; Cuomo et al., 1998], the clinical consequences of ongoing and active infections with both
EBV and HHV-6 remain unknown. Co-infection withthese viruses or other infectious agents may contributeto the pathogenesis of certain diseases including CFS[Komaroff, 1988; Sairenji et al., 1995] and multiple sclerosis [Hollsberg et al., 2005].
Acute EBV infection and prevalence is usuallyassessed by detection of antibodies against three different antigens: viral capsid antigen (VCA), nuclear antigen (NA), and early antigen (EA). EBV PCR testing is
also available to support the diagnosis of acute infection
or reactivation. For HHV-6, IgG, and IgM antibodies
may be used to establish whether an individual is acutely or chronically infected. HHV-6 PCR DNA testing isavailable to support further acute infection, reactivation, or chromosomally integrated virus in selectpatients. IgM antibodies are inappropriate to diagnose
reactivation as their levels wane within months of the
primary infection and do not change or reappear withreactivation. Unfortunately, the presence of IgG does
J. Med. Virol. DOI 10.1002/jmv

Watt et al.

not distinguish viral reactivation from primary infection. Thus, for the suspicion of reactivation, an increaseof or ‘‘high’’ IgG titers can only be used as an indirect
evidence of reactivation. This makes identifying patientswith reactivated EBV or HHV-6 infection challenging.
The seroprevalence for EBV and HHV-6 is 90% or
greater in the adult population, and most individuals
undergo asymptomatic seroconversion. This high seroprevalence complicates the interpretation of serologicaltests in diagnosing reactivation and emphasizes the importance of using supplementary laboratory-based diagnostic tools to detect reactivation. While plasma DNA
is a valid marker for reactivation in immunosuppressed(e.g., transplant) patients, it is unknown if reactivatedinfection in immunocompetent individuals may be present with detectable plasma nucleic acid levels [Levequeet al., 2011]. In healthy, EBV-seropositive subjects, humoral immunity has been demonstrated to remain stable over time with episodic reactivation occurring at alow rate [Amanna et al., 2007].
Valganciclovir has been reported to be effective clinically for treating CFS patients with positive serologies for HHV-6, EBV, and/or cytomegalovirus (CMV).
Seventy-ﬁve percent of patients positive for these viruses who were treated with valacyclovir and/or valganciclovir for at least 6 months improved by 1
point on the Energy Index Point Score (EIPS), representing a signiﬁcant change in functioning [Lerner
et al., 2010].
Twelve patients who were infected chronically with
HHV-6 and EBV and had elevated HHV-6 and EBV
antibody titers (median titers: EBV VCA IgG 1:2,560;
HHV-6 IgG 1:1,280) and suffered from debilitating fatigue for at least 1 year were reported previously toexperience signiﬁcant improvement in their fatigue
and cognitive symptoms following the open-label administration of valganciclovir for 24 weeks [Kogelnik
et al., 2006]. High titers were postulated to indicate
active viral replication and possibly an abnormal immune response.
In this study, a retrospective chart review of 61
patients who met the CFS case deﬁnition [Fukuda
et al., 1994] was performed in which laboratory results,
patient self-reported data, and clinical observations
were analyzed to determine whether antibody titers to
HHV-6 IgG, EBV VCA IgG, EBV NA IgG, and EBV
EA IgG were associated with response to valganciclovir
treatment. Patients with high baseline antibody titers(HHV-6 IgG 1:320, EBV VCA IgG 1:640, and EBV
EA IgG 1:160) were hypothesized to be more likely torespond. Secondary and exploratory analyses of physical and cognitive functioning levels, change in antibody
titers with treatment, age at treatment, fatigue duration, and treatment duration were conducted.
MATERIALS AND METHODSPatient Selection
A retrospective chart review was performed on all
records of 70 CFS patients who had been treated with

HHV-6 and EBV Antibody Titers in CFS

valganciclovir at Stanford University Medical Center
between February 2004 and January 2009. The inclusion criteria were: (i) meeting the CDC CFS case deﬁnition [Fukuda et al., 1994], (ii) prior valganciclovir
treatment, and (iii) complete records for self-reported
functioning levels and antibody titers. Complete
records required baseline and ﬁnal cognitive andphysical functioning levels as well as baseline and ﬁnal antibody titers for HHV-6 IgG, EBV VCA IgG,
EBV NA IgG, and EBV EA IgG. A total of 64 patients
met these criteria. Of this total, six participants did
not have ﬁnal titer measurements; however, thesepatients were included because their data were complete for the primary endpoint. As a result, the study
excluded these six patients in the secondary analyses
involving ﬁnal titers and change in titer (Fig. 1).
Three of the 64 patients in this analysis were included
in a prior study [Kogelnik et al., 2006], and were
therefore excluded, leaving a ﬁnal sample size of 61.
Patient information was obtained from chart records
and direct patient inquiry. Patient demographics (e.g.,
ethnicity, sex, age) were not used for inclusion.
Valganciclovir Treatment
Patients followed one of two valganciclovir treatment regimens based on clinical judgment (e.g., history of side effects to antimicrobials). Fifty-eightpatients took 900 mg of valganciclovir twice daily (induction dose) for 3 weeks, followed by 900 mg of valganciclovir once daily (maintenance dose). Six
patients only took the maintenance dose for the duration of their treatment.
The length of treatment varied among patients
according to the treating physician’s clinical judgment. If patients were treated with valganciclovir
more than once and the two treatment regimens weremore than 1 month apart, then the ﬁrst treatment

1969

regimen was used for analysis as well as for establishing baseline and ﬁnal functioning levels and antibody
titers. If, however, multiple treatments with valganciclovir were <1 month apart, these were considered asingle treatment course for analysis purposes.
EBV and HHV-6 Antibody Titers
Baseline and ﬁnal titers were recorded for HHV-6
IgG, EBV VCA IgG, EBV NA IgG, and EBV EA IgG
before and after treatment with valganciclovir. To
limit variation introduced by using multiple laboratories, all antibody titers were measured by using an
immunoﬂuorescent antibody (IFA)-based assay performed by Focus Diagnostics (Cypress, CA). Titers
were reported as reciprocal dilutions. Since the distribution showed marked skew, titers were natural logtransformed to allow for statistical comparison between dilutions (Appendix 1). For sensitivity analyses,
non-parametric Wilcoxon-signed rank tests wereconducted.
Baseline antibody titers were deﬁned as the highest
titer within 1 year prior to starting treatment. The
highest titers prior to treatment (rather than the average of all available titers) were chosen because hightiters of a certain threshold were considered to havethe greatest pathological impact and because EBV
titers have been shown to be remarkably stable overlong-term follow-up of healthy individuals [Amanna
et al., 2007]. Final titers were deﬁned as those closest
to the cessation of treatment but no later than
6 months after stopping treatment. If no such value
existed, ﬁnal titers were deﬁned to be those closest to
the end of treatment up to 1 month prior to stopping
treatment.
For qualitative analysis, baseline antibody titers
were categorized as high or low. The threshold forhigh baseline titers was deﬁned as HHV-6 IgG
1:320, EBV VCA IgG 1:640, and EBV EA IgG
1:160. All three antibodies were required to meetthese deﬁned thresholds. These criteria were chosen
based on the authors’ clinical experience with evaluating antibody titers of CFS patients. Since prior research has not explored the clinical signiﬁcance for
EBV NA IgG titers in CFS patients, EBV NA IgG
titers were not used for assigning baseline titer category but were still included in analyses to explore potential signiﬁcance.
Physical and Cognitive Functioning

Fig. 1. Patient ﬂow. The number of patients that met the inclusion criteria for primary and secondary analyses.

To assess response to treatment, self-reported physical and cognitive functioning levels were obtained atevery clinic visit. Functioning levels were evaluatedon a scale of 0–100%. A score of 100% indicated thatthe patient was completely well.
Baseline physical and cognitive functioning levels
were determined by averaging up to three levels within 1 year prior to starting valganciclovir treatment.
Final functioning levels were determined by identifying the highest level within 6 months of stopping
J. Med. Virol. DOI 10.1002/jmv

1970

Watt et al.

treatment. The highest levels after treatment (rather
than the average of all available levels) were chosen
in order to capture the largest effect of treatment onfunctioning. Additionally, a wide variation in time totreatment beneﬁt was observed (e.g., functioning may
improve during treatment course or after treatment
cessation). The average of post-treatment functioning
levels, therefore, may not present an accurate depiction of improvement.
For qualitative analyses, a responder was deﬁned asa patient with a self-reported physical or cognitive
functioning increase after treatment of at least 30%.
To explore the distinction between those who respondphysically and those who respond cognitively, responders were further categorized as physical and/or cognitive responders (i.e., physical responders reported atleast 30% improvement in physical functioning, cognitive responders reported at least 30% improvement
in cognitive functioning). Non-responders improved<30% physically and cognitively. Quantitative analysis was performed on change in physical and cognitive
functioning levels independent of response category(responder/non-responder).
Statistical Methods
Three primary analyses were conducted. The ﬁrst
assessed the relationship between baseline antibody
titers and response to treatment. For this, four unadjusted logistic regression models using natural logtransformed antibody titers for HHV-6 IgG, EBV VCA
IgG, EBV NA IgG, and EBV EA IgG were used to predict response to valganciclovir treatment. For each ofthese predictors, an adjusted model was also built tocontrol for sex, age at treatment, and fatigue duration. The secondary analysis used paired t-tests toassess change in mean self-reported physical and cognitive functioning with valganciclovir treatment. Asa tertiary exploratory analysis, differences in mean
antibody titer levels before and after treatment
were compared with one-sample t-tests with a null

hypothesis of no change. Two-sample t-tests wereused to assess the amount of change in each antibody
titer between responders and non-responders.
Additional analysis, such as contrasts in demographics, used one or two-sample t-tests or chi-square
tests as appropriate. Statistical signiﬁcance on all
tests was set at P < 0.05. All statistical analyses were
performed using SAS version 9.2 with SAS Enterprise
Guide version 4.22 on Microsoft Windows XP.
Ethics Approval
This study was reviewed and approved by the
Stanford University Institutional Review Board.
Exemption for informed consent was granted given
the retrospective, chart review study design. All components of this study were conducted in compliancewith local, state, and federal laws, institutional regulations and policies, and the ethical standards of the
Declaration of Helsinki.
RESULTS
Baseline Characteristics
The CFS patients studied consisted of 42 females(69%) and 19 males (31%). The subjects varied widelyin age, duration of fatigue prior to valganciclovir
treatment, and length of treatment (Table I).
Thirty-ﬁve patients (57%) were considered to havehigh baseline antibody titers. Older age (P ¼ 0.0323)
and longer fatigue duration (P ¼ 0.0364) were associated with higher baseline titers (Table I). No signiﬁcant difference was found between baseline titercategory with respect to sex.
Association of Baseline Titers and Response
Thirty-two patients (52%) were categorized as responders. Of the responders, 19 patients (59%)
responded physically and 26 patients (81%) responded
cognitively. Neither unadjusted nor adjusted logistic
regression of the natural log of baseline antibody

TABLE I. Patient Characteristics and Effect of Valganciclovir Treatment on Physical and Cognitive Functioning by
Antibody Titer GroupAll patients (n ¼ 61),
mean (SD)P-valuea

High titers (n ¼ 35),
mean (SD)Low titers (n ¼ 26),
mean (SD)P-valuebAge at treatment, year
Fatigue duration, year
Treatment length, month

47 (14)12 (10)6.5 (2.0)51 (13)14 (12)
6.7 (2.2)

43 (15)8.8 (7.5)
6.2 (1.9)

0.03230.0364NS

All responders, %Physical responders, %Cognitive responders, %Physical functioning change, %Cognitive functioning change, %

52
31
43
þ19 (22)þ23 (21)623251
þ20 (21)þ26 (19)4133
33
þ18 (23)þ19 (23)

NS
NS
NS
NS
NS

<0.0001<0.0001SD, standard deviation; NS, not signiﬁcant.
aThis P-value refers to the signiﬁcance of the change in physical and cognitive functioning after treatment for all patients.
bThis P-value refers to the signiﬁcance of the difference in the indicated values between patients in the high titer group and the low titergroup.

J. Med. Virol. DOI 10.1002/jmv

HHV-6 and EBV Antibody Titers in CFS

1971

titers was statistically associated with response totreatment. An analogous analysis showed that there
was no signiﬁcant difference in mean baseline antibody titers between responders and non-responders(Table II). There was no signiﬁcant difference in meanchange of physical and cognitive functioning between
high and low baseline antibody titer categories(Table I).
Changes in Physical andCognitive Functioning
Before valganciclovir treatment, the average baseline physical and cognitive functioning levels were34% (standard deviation; SD 6.9%) and 43% (SD5.4%), respectively, for all patients (responders andnon-responders). After treatment, the mean of all
patients’ physical and cognitive functioning levels improved by an average of 19% (P < 0.0001) and 23%(P < 0.0001), respectively (Table I, Fig. 2a–c). The
mean change in physical and cognitive functioning
levels was þ34% (SD 19%) and þ37% (SD 18%), respectively, in the responder group and þ3.1% (SD10%) and þ7.7% (SD 10%), respectively, in the nonresponder group.
Change in Titers
Mean antibody titers for EBV VCA IgG(P ¼ 0.0165) and HHV-6 IgG (P < 0.0001) decreased
with valganciclovir treatment in all patients (responders and non-responders). No signiﬁcant difference wasfound in the change of antibody titers after treatment
between the responder and non-responder groups(Table II).
Responder Status
No signiﬁcant difference was found between responders and non-responders with respect to sex andbaseline titer category (high/low). However, longer
treatment length was associated with the respondergroup (P ¼ 0.0002). There was no signiﬁcant difference between responders and non-responders withregard to age at treatment and fatigue duration(Table II).
DISCUSSION
The patients in this study had a mean age of
47 years at the time of treatment and 70% were female, an age and sex distribution representative ofthe larger CFS population in the United States [Jasonet al., 1999]. All patients improved by a mean 19%
and 23% in physical and cognitive functioning, respectively, after valganciclovir treatment (P < 0.0001).
For responders, the mean physical and cognitive improvement was 34% and 37%, respectively. The standard deviation of patients’ baseline physical andcognitive functioning levels was notably very low compared to the signiﬁcant mean improvement in functioning levels after treatment, emphasizing thesigniﬁcant recovery. It was, however, not possible toassess the possibility of placebo or Hawthorn effects
due to the single-arm, historical study design.
A 2010 study used a different validated scale formeasuring severity of fatigue, the Energy Index Point
Score (EIPS) [Lerner et al., 2008]. The EIPS ranks fatigue on a scale from 0 to 10, and an improvement ofat least 1 point qualiﬁes a patient as a responder[Lerner et al., 2010]. In comparing this study’s physical and cognitive functioning scale to the EIPS, achange of 1 point out of 10 would be loosely comparable to a 10% improvement. However, this study categorized only those patients whose physical or
cognitive functioning improved at least 30% as responders. If this study had used a similar responder
deﬁnition, the change would have yielded a muchhigher proportion of responders than non-responders
than is currently reported in this study. In the context

TABLE II. Patient Characteristics, Baseline Physical and Cognitive Functioning and Antibody Titers, and Change inPhysical and Cognitive Functioning and Antibody Titers After Valganciclovir Treatment by Responder GroupAll patients(n ¼ 61),
mean (SD)Age at treatment, year
Fatigue duration, year
Treatment length, month
Baseline EBV VCA
Baseline EBV NA
Baseline EBV EABaseline HHV-6
EBV VCA change
EBV NA change
EBV EA change
HHV-6 change

47 (14)12 (10)6.5 (2.0)
7.7 (2.0)
5.1 (1.5)5.6 (1.5)
6.5 (1.5)
0.47 (1.4)
0.18 (1.3)
0.29 (1.1)
0.86 (1.2)

P-valuea

Responders(n ¼ 32),
mean (SD)

Non-responders(n ¼ 29),
mean (SD)P-valueb

0.0165NS
NS<0.000149 (12)
12 (11)7.4 (2.4)
7.9 (1.3)
5.1 (1.2)
5.7 (1.1)
6.5 (1.3)
0.67 (1.1)
0.13 (1.3)
0.49 (1.0)
0.67 (1.4)

45 (16)
12 (9.4)
5.5 (0.9)
7.4 (2.5)
4.9 (1.8)
5.4 (1.8)
6.6 (1.6)
0.26 (1.7)
0.24 (1.3)
0.12 (1.1)
1.1 (0.97)

NSNS
0.0002
NS
NS
NS
NS
NS
NS
NS
NS

Unadjusted
OR (CL)

Adjusted
OR (CL)

1.1 (0.86–1.5)
1.1 (0.77–1.5)
1.2 (0.81–1.6)
0.96 (0.68–1.4)

1.1 (0.81–1.5)
1.0 (0.72–1.5)
1.1 (0.78–1.7)
0.86 (0.59–1.3)

SD, standard deviation; OR, odds ratio; CL, conﬁdence limit; NS, not signiﬁcant.
aThis P-value refers to the signiﬁcance of the change in titers after treatment for all patients.
bThis P-value refers to the signiﬁcance of the difference in the indicated values between responders and non-responders.

J. Med. Virol. DOI 10.1002/jmv

1972

of the literature and given the difﬁculty that most
CFS patients have attaining any level of recovery,
these ﬁndings are clinically striking and suggest thatvalganciclovir treatment may result in substantial
improvement in physical and/or cognitive functioningin CFS patients with positive HHV-6 and EBV antibody titers.
In contrast to this study’s original hypotheses, there
was no statistically signiﬁcant association between

Watt et al.

baseline antibody titers and response to valganciclovir
treatment. The high baseline titer group exhibited atrend toward increased physical and cognitive improvement. Fifty-one percent (51%) of patients withhigh titers were cognitive responders compared to only
33% of those with low titers. Based on these trends,
higher baseline EBV titers may still correlate with improved response to valganciclovir. Furthermore, after
completion of this study an evaluation of 50 healthy
individuals was found to have a median EBV VCA IgG
1:640, EBV EA IgG 1:160, and HHV-6 IgG 1:160 (personal communication from Focus Diagnostics, Inc. to
J.G.M.) The pure effect of baseline antibody titer on
clinical improvement or the modest magnitude of baseline antibody titers in this study may not be large
enough to detect an effect with this sample size, as individual antibody titers can vary by two dilutions under normal circumstances. Furthermore, somepatients with reactivated virus may have borderline
hypogammaglobulinemia. In these patients, a low viral
IgG may actually represent a signiﬁcant relative proportion of total IgG. Conversely, patients with notably
strong immune systems may have more robust serological responses. Larger, prospective studies are needed
to substantiate the small effect observed in this study
and to look for non-linearities (e.g., thresholds) inantibody titer level that may predict response totreatment.
Valganciclovir treatment caused all mean antibody
titers to decrease in responders and non-responders.
The decline in both EBV VCA and HHV-6 antibody
titers observed in this open-label cohort suggests thatour patients might have had a substantial reactivation that was amenable to antiviral intervention
against both viruses. The decline in EBV VCA andEBV EA antibody titers was more pronounced in responders than non-responders; however, this distinction was not statistically signiﬁcant. This study was
not powered to detect signiﬁcant differences in themean change between these groups.
With regard to age at treatment and fatigue duration, there was no signiﬁcant difference between
responders and non-responders. However, longer
treatment duration was associated with improved responder status, which suggests that longer treatment

Fig. 2. a: Change in physical functioning for each patient (n ¼ 61).
Change in each patient’s physical functioning on a 0–100% scale frombaseline to end of valganciclovir treatment. Each solid line represents
one patient. Dashed line indicates mean change over treatment period. b: Change in cognitive functioning for each patient (n ¼ 61).
Change in each patient’s cognitive functioning on a 0–100% scalefrom baseline to end of valganciclovir treatment. Each solid line represents one patient. Dashed line indicates mean change over treatment period. c: Distribution of change in functioning (n ¼ 61).
Distribution of change in physical and cognitive functioning on a 0–
100% scale after valganciclovir treatment for all patients. Withineach box, the diamond represents the mean and the line indicates themedian change in functioning level. The lower limit of each box indicates the 25th percentile and the upper limit indicates the 75th percentile of change in functioning level. The lower whisker outside eachbox indicates the minimum change in functioning level and the upper
whisker indicates the maximum change in functioning level.

J. Med. Virol. DOI 10.1002/jmv

HHV-6 and EBV Antibody Titers in CFS

may improve the likelihood of responding to valganciclovir. Decisions on treatment duration were made on
an individual basis between the physician and patient, which may bias the relationship between treatment duration and response. Future randomization ofpatients to different treatment durations is needed to
conﬁrm these ﬁndings and to assess if there is a linear
duration–response correlation. CFS patients with herpesvirus infections on antiviral medication continue
to experience beneﬁt for at least 2–3 years while ontreatment [Lerner et al., 2010].
This study has several limitations. Because it is aretrospective study, this report has the limitation of
excluding nine patients who did not meet the inclusion criteria. The absence of a control population inthis study makes it impossible to draw deﬁnitive conclusions regarding treatment effect. Prospective, randomized, double-blind, placebo-controlled studies areneeded to explore the clinical relevance of theseﬁndings.
While self-report assessments are not an ideal toolfor evaluating CFS patients’ functioning levels, theauthors’ research and clinical experience have demonstrated that this system of self-reported assessments
is an informative measure of physical and cognitive
functioning. Though self-reported baseline and ﬁnalfunctioning levels may have inter-rater variability,
this study addressed this problem by evaluating
intra-rater change in functioning and contrasted only
the inter-rater magnitude of change to evaluate treatment efﬁcacy.
In the context of current research, the magnitudeof physical and cognitive improvement after valganciclovir treatment was substantial. These ﬁndings
emphasize the importance of developing tools to selectcandidates for valganciclovir treatment who are likely
to respond. Identifying factors predictive of response
prior to treatment initiation will enable providers toprescribe valganciclovir or other antiviral interventions effectively to CFS patients. While this study
was underpowered to conduct hypothesis testingon the differences between responders and nonresponders, it suggests that valganciclovir can beassociated with self-rated improvement in physicaland cognitive functioning in a subset of CFS
patients.
ACKNOWLEDGMENTS
We would like to thank the patients in the Stanford
CFS Clinic for their patience and willingness to bepart of efforts to enhance the understanding andtreatment of this unexplained illness. The authors
also thank Manisha Desai, Ph.D. for her criticalreview of the article and thoughtful suggestions
for statistical analysis. M.R.L. was supported by the
Stanford University School of Medicine Molecular
Basis of Medicine Scholarly Concentration and
the Stanford University School of Medicine Medical
Scholars Fellowship Program.

1973

APPENDIX 1
TABLE A1. Natural Log (LN) Transformation of EBV and
HHV-6 IgG Antibody Titers
EBV VCAEBV NAEBV EA

HHV-6

LN

1:10
1:20
1:40
1:80
1:160
1:320
1:640
1:1,280
1:2,560
1:5,120
1:10,240
1:>10,240a

1:10
1:20
1:40
1:80
1:160
1:320
1:640
1:>640a

1:10
1:20
1:40
1:80
1:160
1:320
1:640
1:>640a

1:10
1:20
1:40
1:80
1:160
1:320
1:640
1:1,280
1:2,560
1:5,120
1:10,240
1:>10,240a

2.30
3.00
3.69
4.38
5.08
5.77
6.46
7.15
7.85
8.54
9.23
9.93

a

These values were rounded up to the next dilution to facilitate
quantitative analysis.

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